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Pfizer shot after AstraZeneca is safe, could induce better immune response, researchers find

India isn’t looking at a mixing option just yet as Pfizer is unavailable in the country so far and there is no data on mixing Covaxin and Covishield.

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New Delhi: Mixing different vaccines may help better protect against Covid-19, with emerging studies showing that vaccinating people with both the Oxford-AstraZeneca and Pfizer-BioNTech vaccines is safe and produces a potent immune response.

Researchers in Spain have conducted a trial on 663 people, who had already received the first shot of the AstraZeneca vaccine (marketed in India as Covishield).

Of these, two-thirds of the participants received the mRNA-based Pfizer vaccine around eight weeks after their jab, instead of getting a second shot of the AstraZeneca vaccine. A control group of 232 people did not receive a booster.

The researchers, led by the Carlos III Health Institute in Madrid, found that the participants who received the mRNA booster vaccine had higher levels of antibodies than participants in the control group.

The antibodies in their blood serum were also able to neutralise the SARS-CoV-2 in lab tests.

The findings were shared on the institute’s website this week, but a study is yet to be published.

Also read: Ready to strengthen dialogue, scale-up tech collaboration with India amid pandemic: IMF

India not looking at vaccine mixing yet

Many states in India are currently going through vaccine shortages to the extent that some have been forced to stop fresh vaccinations in the younger age groups. But the working group of the National Technical Advisory Group on Immunisation (NTAGI), which is looking at evidence on Covid vaccines, isn’t considering mixing vaccines just yet.

Dr N.K. Arora, who heads the committee, told ThePrint: “I am aware of the Spanish study and it is a good study. But it is about mixing the Pfizer vaccine with Covishield. We do not have Pfizer in India yet. The only two vaccines that we have are Covaxin and Covishield and there is no evidence yet on their mixing. So we are not looking at mixing at the moment.”

The Government of India is in talks with Pfizer but the company has so far not tied up with any Indian company for manufacturing.

Unless the vaccine is manufactured in India, the Government of India will not procure it for the national programme, according to the new policy in place from 1 May.

Mixing vaccines is an accepted strategy

The strategy of mixing different vaccines is known as a heterologous prime and boost, which has been used for vaccines against other diseases, such as Ebola and HIV.

The Spanish study comes a week after a group of researchers from the Oxford University reported in the Lancet journal that mixing the vaccines was safe.

“These responses look promising and show the potential of heterologous prime-boost regimens,” Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, Massachusetts, was quoted as saying in a Nature report.

Zhou Xing, an immunologist at McMaster University in Canada, said the antibody response to the Pfizer boost seems to be stronger to what is observed in people receiving two doses of the Oxford-AstraZeneca vaccine.

Also read: For vaccine-starved countries like India, delaying second dose turns to be a winning strategy


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